In the case of the storage or transmission of moving images, it is frequently necessary to reduce the large number of information items by means of suitable compression methods. Methods for movement estimation, which utilize the correlations between individual images, are used for this purpose.
In order to estimate the movement, the image to be coded is split into blocks and each of these reference blocks are compared with blocks of the same size within a sub area of a preceding or subsequent image, the so-called search window. The sum of the absolute values of the differences between the pixel values of the reference block and the corresponding pixel values of the search window is used, for example, in this case as the comparison criterion (cost function). A movement vector, which indicates the offset of these blocks calculated in pixels, is determined for each reference block for that block in the search window which in each case provides the best correspondence. As a result of this movement estimation, only the reference image is required for the movement compensation of the complete image, and the associated movement vector for each reference block. In general, exact reconstruction does not, of course, take place.
Known methods for movement estimation use all the pixels in the reference block and in the search area (full pel full search) in order to find the optimum movement vector having the smallest cost function. However, this method requires very fast, and thus expensive, hardware.